1. Field of Invention
This invention relates to a rod sealing system for a hydraulic cylinder, and more specifically to a rod sealing system having a back-up rod seal and a method of providing back-up rod sealing protection.
2. Description of Related Art
Hydraulic cylinders have a variety of uses and are well known in the art. One conventional design of a hydraulic cylinder has a piston rod which extends to through the cylinder head and is sealed by means of a two seals. The primary seal which is located closer to the working or operating chamber of the piston is a ring which consists of a rubber or another material having a stable shape, for instance a synthetic material having the respective characteristics. The primary seal is wear resistant but not free of leakage. In some applications, an annular collecting groove may be provided between the primary seal and the secondary seal to collect the leakage oil which is not held back by the primary seal. The leakage oil can be drained from the annular collecting groove by means of a leakage oil conduit extending from the annular collecting groove. Alternately, the leakage oil leaks past the secondary seal and onto the machinery or the ground.
With prolonged use, the primary seal begins to wear and more and more fluid will leak by the primary seal. In time, the primary seal becomes so worn that too much fluid leaks around the seal and overwhelms the low pressure secondary seal. When this happens the fluid will leak around the rod and onto the cylinder and beyond. This leakage of hydraulic fluid can cause various environmental and safety concerns. Ultimately, the cylinder needs to be removed from service and the seal replaced. This leads to down time of the working machinery, and if it occurs at an inopportune time, the cost in downtime can be substantial.
It would be desirable to provide an improved hydraulic cylinder having a rod seal that has an extended life with a back-up seal without significant compromise of performance.